2001/05/10 by K O'Brien, K. O'Brien, K. Horne +13
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2001.04651.x
published as Mon.Not.Roy.Astron.Soc. 326 (2001) 1067 · 10 pages, including 6 figures, accepted for publication by MNRAS
arxiv created 2001/05/10 · openalex publication_date 2001/09/21 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present Keck II spectroscopy of optical mHz quasi-periodic oscillations (QPOs) in the light curve of the X-ray pulsar binary Hercules X-1. In the power spectrum it appears as ‘peaked noise’, with a coherency ∼2, a central frequency of 35 mHz and a peak-to-peak amplitude of 5 per cent. However, the dynamic power spectrum shows it to be an intermittent QPO, with a lifetime of ∼100s, as expected if the lifetime of the orbiting material is equal to the thermal time-scale of the inner disc. We have decomposed the spectral time series into constant and variable components and used blackbody fits to the resulting spectra to characterize the spectrum of the QPO variability and constrain possible production sites. We find that the spectrum of the QPO is best fitted by a small hot region, possibly the inner regions of the accretion disc, where the ballistic accretion stream impacts on to the disc. The lack of any excess power around the QPO frequency in the X-ray power spectrum, created using simultaneous light curves from RXTE, implies that the QPO is not simply reprocessed X-ray variability.